[Setup]
AppId={{87E1AD40-F32B-4EF7-A2FF-5B508814068A}
AppName=My Program
AppVersion=1.5
DefaultDirName=My Program

[INI]
Filename: "{app}\UserInputs.ini"; Section: "Language"; Key: "Language"; String: "{language}"
Filename: "{app}\UserInputs.ini"; Section: "Registration"; Key: "ApplicationID"; String: "{code:GetAppId}"

[Code]
// this is a helper function (actually a getter for the above INI section entry parameter),
// which we need to strip out the "{}" chars before we pass the value to the [Registration]
// section's ApplicationID key
function GetAppId(Value: string): string;
var
  S: string;
begin
  // here is the same code as in my last answer, just returned as this getter function
  // result
  S := '{#SetupSetting("AppId")}';
  Result := Copy(S, 3, Length(S) - 3);
end;